1. Intraspecific Population Regulation
Chapter 11
Intraspecific Population Regulation

2. I. Population growth curves
No population grows indefinitely
Will confront the limits of environment
Most do not grow exponentially
Interactions tend to regulate population’s size

3. II. Regulation by growth mechanisms
Density-dependence = regulation by mechanisms controlled by size of population
Density-independence = effects of influence do not change with population density

4. 1. Density-dependent Effect increases as population size increases
No influence at low density
Larger population / more individuals affected
Largely through competition for resources

5. 2. Density-independent Effects do not change with population density
Proportion of individuals affected –same at any density
Can have significant impact on populations
Can mask or eliminate density-dependent regulation

6. III. Competition Among same species individuals for resources
One aspect of population regulation
2 kinds of competition
Scramble competition—no one receives enough of the resource
Contest competition—some claim enough and deny others a share

7. Scramble competition—produces chaotic oscillations in populations
Limited resource will cause species to exhibit only one type of competition
Scramble competition—produces chaotic oscillations in populations
Wastes resources—limits average density to below carrying capacity of habitat
Contest competition—causes a fraction to suffer (unsuccessful individuals)
Eliminates waste of resources
Permits maintenance of high density

8. Biomass—a function of accumulated living tissue
As populations increase toward insufficient resources, scrambling competition reduces food intake.
this slows growth and limits reproduction
seen in overstocking of fish
vertebrates fecundity affected
Biomass—a function of accumulated living tissue
can be few large or many smaller individuals

9. IV. Aggression High density causes stress
Aggressive contacts increases
Stress triggers hyperactivation endocrine glands
Suppresses growth, reproduction and immune system

10. V. Coping with stress Pheromones encourage or inhibit reproduction
Seeking new vacant habitat—dispersal
Success rate low
Few arrive at suitable habitat and flourish
Dispersal before resource depletion is important with low density

11. VI. Dispersal
Individuals dispersed are normally in good condition, either sex, any age—good chance of survival
Relocation habitats have increased resources + breeding sites, decreased competition
Distance relative to availability of habitat
Requires a source and sink

12. VII. Social issues of populations
Social behavior limits populations:
Surplus animals, not breeding, or attempting and failing
Prevented from breeding
Removal of dominant animals results in breeding of surplus animals
Breeding animals not using all space or food

13. Social organization Common in populations
Based on aggressiveness, intolerance and dominance of one over another
2 opposing forces at work
Mutual attraction
Negative reaction against crowding and need for personal space

14. Simple social organization
Alpha individual—dominant over all
Beta—dominant over all except alpha
Omega—subordinate to all
Rankings established by fighting, bluffing, threatening
Ranking maintained by habitual subordination and punishment
Important for populations—stabilizes intraspecific competition
Resolves disputes with minimal energy

15. IX. Movement and distribution
The space occupied during a year = home range
May differ with sex
Not defended
Range defended = territory
Varies with availability of food
Size of territory
Carnivores > herbivores/omnivores
Dominant > subordinate
Males > females
Adults > subadults

16. Territoriality Animal defends exclusive area no shared with rivals
Occurs in regular patterns of distribution
Costly in energy and time
May interfere with breeding, feeding and rearing of young
Quality territory = dominant male
Floating reserve—evicted individuals

17. X. Territory vs home ranges
Indicates the carrying capacity
Management becomes ecological/economical problem
Plants can be territorial
Shading and competition for nutrients
Release of organic toxins

18. XI. Review
Density dependent influences population growth and fecundity
Density independent factors may be more important
May eliminate density dependent factors
May go beyond a limit of tolerance